Stroke, physical injury, and disease are causes of impairment of motor function involving one or more limbs. It is often possible to recover some motor function through rehabilitation, and practicing functional multi-joint movements with the impaired limb is an important part of motor recovery (Dobkin, 2004). Current therapeutic techniques therefore focus on training with repetitive, frequent functional movements (Teasell et al., 2003).
Providing patients with the attention they need is a challenge. Each patient requires extensive one-on-one attention, and therapy programs are physically exhausting for the therapist. The use of robotic devices to provide therapy would improve efficiency and effectiveness of the therapy, and this has been at the forefront of recent stroke rehabilitation research (Hesse et al., 2003; Reinkensmeyer et al., 2004). Robots not only have the ability to provide repetitive functional movement training, but also can provide sensitive and objective quantitative assessments of movement. The technology also makes it possible for a single therapist to supervise multiple patients simultaneously.
Existing robots for upper limb rehabilitation and assistance include MIT-MANUS (Krebs et al., 1998), MIME (Burgar et al., 2000), GENTLE/s (Loureiro et al., 2003), MULOS (Johnson et al., 2001), T-WREX (Sanchez et al., 2004; ARMEO (available from Hocoma AG, Switzerland); Sanchez et al., 2006), ARMin (Mihelj et al., 2006; Mihelj et al., 2007), and KINARM™ (Scott, 1999), among others. Exoskeleton robotic devices have the advantage of direct control over limb joint function, which allows independent control of each DOF of the limb. This ensures that compensatory movements by a subject can be monitored and/or prevented. A drawback of exoskeleton devices is that coupling of the robotic linkage to the subject's limb requires alignment of the axes of the limb joint and the corresponding robot joint. With current exoskeleton robots, this results in parts of the robot being located close to the subject, which may be intimidating to some subjects.
A further drawback of current robotic devices is that they cannot match the full mobility of the human upper limb. This is particularly true for the shoulder complex because it has a compact arrangement of five major degrees of freedom (DOF): two at the sternoclavicular joint and three at the glenohumeral joint. The glenohumeral joint can be approximated as a ball-and-socket joint and has been replicated in some current devices. However, the shoulder girdle has been neglected, despite its importance in stabilizing and orienting the upper limb. Without direct control at the sternoclavicular joint, it is not possible to prevent the subject from making compensatory movements, nor is there a way to properly regain strength and coordination of the shoulder girdle.